The mechanism of inter- and intracellular diffusional transport by vesicles in living organisms is
poorly understood at the molecular scale. The diffusion of submicron and nanoparticles in dense
media has been treated by numerous theoretical models. We face this problem experimentally using
Mössbauer spectroscopy. On a characteristic for this method narrow time scale (≈10^−7 s), the velocity
distribution of 120 nm spherical Fe2O3 particles suspended in a 60% water solution of sucrose was
determined by analyzing the 57Fe Mössbauer spectral line profile. The particles usually exhibit classical
Brownian motion, but their main diffusion mechanism is related to infrequent ( f≈10^6 1/s) but
distant (d≈1 nm) translations. During such movements, the particles experience a minimal friction
described by the temporal local viscosity, ηloc≈28 μPa·s.
